A railroad track may deform vertically or horizontally under the train loads. Upon reliable detection of such deformation (irregularities), the track must be controlled within predetermined standards for maintenance, thereby maintaining the safety or comfortable ride of the trains.
The irregularities of the railroad rails include horizontal irregularity (alignment irregularity), vertical irregularity (longitudinal level irregularity), irregularity in interval between right and left rails (gauge irregularity), a difference in height of the right and left rails (cross level irregularity), and twisting of a rail track (twist irregularity). In order to calculate such irregularities of the rails, an apparatus for detecting the rail displacement is used that irradiates the rails with spot light when installed on a vehicle traveling along the rails (see, for example, Patent Literature 1).
FIG. 10 depicts a displacement detecting apparatus 210 as disclosed in Patent Literature 1, which includes two sets of two displacement detectors 202, 203 for emanating spot light for respective rails 201 to irradiate upper surfaces and inner side surfaces thereof after the spot light has reflected off respective mirrors 204, 205. The displacement of the rails 201 is detected based on the light with which the upper surfaces and the inner side surfaces of the rails 201 have been irradiated using a triangulation method.
Each of the right and left sets of the displacement detectors 202, 203 is fixedly mounted on a housing 206 of the displacement detecting apparatus 210. On the other hand, the angles of inclination of the mirrors 204, 205 for reflecting light can be regulated to measure the same positions on the surfaces of the rails 201. During the measurement, the same points on the surfaces of the rails 201 are continuously irradiated with the light by appropriately controlling the angles of inclination of the mirrors 204, 205. A device for controlling the mirrors 204, 205 in such a way is referred to as a servo mechanism (not shown). In the motion control of the mirrors 204, 205 by the servo mechanism, the angles of the mirrors 205 corresponding to the horizontal displacement detectors 203 are regulated based on positional data of the rails 201 obtained from the vertical displacement detectors 202, and the angles of the mirrors 204 corresponding to the vertical displacement detectors 202 are regulated based on positional data of the rails 201 obtained from the horizontal displacement detectors 203. The displacement detectors 202, 203, the mirrors 204, 205 and the servo mechanism are collectively referred to as a measurement unit 211.
The displacement detecting apparatus 210 is fixed to a railroad vehicle through the housing 206, but because springs are interposed between the vehicle and wheels, a vehicle running motion may cause the housing 206 and the displacement detecting apparatus 210 to have a position difference with respect to the rails 201, thus giving rise to measurement errors. In order to avoid such errors, a self-position detector 207 is installed at the center of the housing 206. The self-position detector 207 is provided with two acceleration meters 208, 209 to measure a rate of acceleration in the vertical direction and that in the horizontal direction. The self-position detector 207 double-integrates the rates of acceleration obtained from the acceleration meters 208, 209 to calculate the displacement of the housing 206 and the self-position detector 207 relative to a preset reference position. The self-position detector 207 is further provided with a gyroscope 212 to measure a horizontal inclination of the housing 206 and the self-position detector 207 relative to a preset reference orientation. Using the displacement and inclination data of the housing 206 and the self-position detector 207 calculated by the self-position detector 207, displacement data of the rails 201 obtained by the displacement detectors 202, 203 are corrected (compensated) for calculation of correct values.